New Asteroid Belt Analogs using WISE

Thesis talk given at the 225th American Astronomical Society meeting in Seattle on newly discovered asteroid belt disks using WISE (see Patel et al. 2014)

Transcript

1. New Asteroid Belt Analogs using WISE Rahul I. Patel AAS 225 Thesis Talk Jan. 8th, 2015 Work done in collaboration with Dr. Stanimir Metchev, Dr. Aren Heinze and Joe Trollo This work is partially supported by NASA Origins of Solar Systems via subcontract No. 1467483 @ripatel_astro
2. QUESTIONS: How many undetected exo-asteroid belts are there in Solar neighborhood? What is the frequency of Solar System analogs? Storyboard: Approach Take advantage of 3-30 µm WISE All-Sky data to search for faint nearby exo-asteroid belt systems.
3. Studying architecture of exo-debris disks places the Solar System in context. Fomalhaut; ~440 Myr; 7.6 pc Kalas+2013
4. Warm dust probes dynamical activity in inner regions. Matthews+2014 by Kate Su
5. Over past 30 years, >1000 IR excesses detected out to 500 pc; ~50%<75pc Spitzer, 2003-Present, 3-180 µm ISO; 1995-1998, 2.5-200µm Akari; 2006-2011 Herschel, 2009-2013, 55-672µm Sky positions for ~900 protoplanetary and debris disk sources
6. Majority have cold dust emission, while a smaller fraction of stars possess warm dust – so then the obvious thing to do is to …
7. search for more systems with warm dust
8. New discoveries from WISE… … enable statistical studies of debris disks
9. SkyView WISE 12 μm IRAS12 μm WISE has greater resolution and sensitivity than IRAS, and greater coverage than pointed surveys.
10. Matthews+2014 by Kate Su WISE mid-IR bands probe dynamical activity in zodiacal dust and asteroid belt regions W4- Excess: W1-W4 W2-W4 W3-W4 W3- Excess: W1-W3 W2-W3
11. Colors over photospheric models to search for IR excess Precise calibration of photosphere required to increase sensitivity to excesses: • SED fits to multi-epoch photometry from different instruments are subject to relative systematic uncertainties. • Not the case for multi-λ data obtained simultaneously. – (e.g. WISE, Spitzer/IRS)
12. Hipparcos Stars within 120 pc and |b|>5o Sample of Main Sequence Stars Significant False-Positive Sources: Projected Companions Stellar Variability Checks Inconsistent WISE measurements Patel+2014, ApJS, 212, 10 (mag) (mag)
13. Our WISE excess search improves upon previous attempts because we: • Apply saturation corrections to include brighter stars. Improved sampling of nearby stars • Empirically calibrate photospheric colors. Increase sensitivity to fainter disks Patel, R., Metchev, S., & Heinze, A., "A Sensitive Identification of Warm Debris Disks in the Solar Neighborhood Through Precise Calibration of Saturated WISE Photometry", 2014, ApJS, 212, 10.
14. Bright stars were included by correcting trend in saturated wings Patel+2014
15. Our WISE excess search improves upon previous attempts because we: • Apply saturation corrections to include brighter stars. Improved sampling of nearby stars • Empirically calibrate photospheric colors. Increase sensitivity to fainter disks Patel, R., Metchev, S., & Heinze, A., "A Sensitive Identification of Warm Debris Disks in the Solar Neighborhood Through Precise Calibration of Saturated WISE Photometry", 2014, ApJS, 212, 10.
16. Calculating photospheric WISE colors Patel+2014
17. 99.5% CL Patel+2014
18. Uncertainty distribution sets false-positive rate 99.5 % CL Patel+2014
19. RESULTS
20. Increased sensitivity to fainter dust = new disks in already scrutinized volume 35% INCREASE IN 10—30 µm excesses within 75 pc Our detections Detections over last 30 years Prior detections Even after a dozen studies using WISE using colors and SED fitting 25% INCREASE IN DISK CENSUS WITHIN 75 PC Prior detections Our detections
21. Verifying Debris Disk Hosts Through A Weighted Combination of WISE Colors Patel+2015, in preparation E[W1-W4] E[W2-W4] E[W3-W4]
22. Single-color excess might be real, even without a weighted excess: • Due to larger uncertainties in W1 and W2 than W3 • if small W3 excess exists
23. Are we detecting warm dust or emission from cold dust?
24. Aggregate of 22 um excesses shows a small amount of 12 um excess  warm dust 12 µm excess significance 12 µm (W3) significances for stars with significant 22 µm (W4) excesses
25. QUESTIONS: How many undetected exo-asteroid belts are there in Solar neighborhood?  Used WISE to identify and verify via weighted combination of colors, >100 new faint disks in 75 pc around bright stars.  Substantial increase in known disk population
26. QUESTIONS What is the frequency of Solar System analogs?  What are the stellar ages?  Are these quiescent evolved planetary systems or young solar system analogues planetary systems?
27. Future Direction Determine ages for stars to determine stage of dust evolution  Spectroscopic data obtained for majority of stars Follow up with direct imaging to spatially characterize dust  e.g., GPI, SPHERE